1. Field of the Invention
The present invention relates to a fixing apparatus that passes a recording material between a fixing roller and a pressurization roller to fix a toner image.
2. Description of the Related Art
In some image forming apparatuses, a down sequence in which, for example, printing speed is decreased or printing interval is widened so as to prevent a decrease in the temperature of a fixing apparatus is performed. For example, regarding a down sequence performed when the temperature of a fixing apparatus has decreased, there has been proposed the technique that the time that elapses before the temperature of the fixing apparatus returns to a fixable temperature is gradually shortened according to the time that elapses after power-on of an image forming apparatus (Japanese Laid-Open Patent Publication (Kokai) No. 2007-183686).
Also, there has been proposed the technique that when the temperature of a fixing roller (heating roller) in an image forming apparatus decreases to a predetermined temperature or lower, it is determined that the temperature of a pressurization roller disposed in opposed relation to the fixing roller has decreased, and the temperature of the fixing roller is uniformly increased (Japanese Laid-Open Patent Publication (Kokai) No. H10-282836).
However, according to technique that the time that elapses before the temperature of the fixing apparatus returns to a fixable temperature as described in Japanese Laid-Open Patent Publication (Kokai) No. 2007-183686, when the power is turned on and off while the fixing apparatus is sufficiently hot, the time required for a down sequence which can originally be short becomes excessively prolonged. As a result, the problem that the productivity of the image forming apparatus deteriorates arises.
Moreover, it may be inappropriate to determine that the temperature of the pressurization roller has decreased based on only an instantaneous temperature status of the fixing roller. For example, problems concerning the fixing apparatus such as temperature increase at an end of the fixing roller or hot offset (double transfer) which occurs when a short sheet is fed in a main scanning direction may arise.